Does anyone have a some test data recording the smoke box temperature of the combustion gases at the exit of the flues?
Alfred Bruce has a diagram listing 625 degrees F for the temperature at the flue exit. I would assume the range is somewhere between 600 to 800 degrees F depending on how hard the locomotive is working. Compared to power plants that use economizers and air preheaters, which bring down the combustion gases down to 350 degrees or so, the steam locomotive dumps incredible amounts of heat out of the stack.
I've been doing some basic combustion calculations based upon a method from Babcock & Wilcox "Steam: Its Generation and Use" in conjunction with data on the April 3, 1943 Big Boy dynamometer tests. One aspect that bothered me is that the inherent losses of combustion are charged against the locomotive, ie heating the nitrogen in air, heat in water vapor from combustion and moisture of fuel, and humidity of ambient air. The inherent losses, with no excess air, amount to 18% of the BTU content of the fuel. Adding radiation loss, unburned losses, 125% air, etc amounts to a energy loss of almost 40%.
Simple math shows that the final efficiency of the locomotive is about 5.5%. 60% of fuel is released in combustion, 80% of that heat released is absorbed by the boiler and superheater, and about 11.5% of the heat in the steam is converted to work.
See tables below for calculations and parameters used, and weather data is from historical records for Ogden, UT and Evanston, WY.
"If a nation expects to be ignorant and free, it expects what never was and never will be." Thomas Jefferson
Couldn't tell you what the temperatures of the smokebox gases were, but whatever they were they were hot enough to blister the paint off the smokeboxes through most of the steam era, hence the graphiting of smokeboxes to prevent corrosion. By the time good heat resisitant paints were available the steam era was just about over.
Hi Burgard 540
That’s an intriguing table , yet it would appear to allow for some marginal points :
Where did you get the , quote >> 125 % air << from ( when with a BB at work usually there was black smoke like a volcanic eruption ) ?
Where did unburnt losses go ( zero in line h ) ? Why boiler efficiency of , quote >> 80 % << ?
Quote >> about 11.5% of the heat in the steam is converted to work << ? What live steam heat content did you calculate with and what was the adiabatic and the polytrophic heat drop , at what amount did you calculate wall effects and influences of cylinder tribology and what was c/o ?
Apart from actual figures , each of these values would describe a certain work point of the engine , so how do you get from there to a general statement of overall locomotive efficiency of , quote >> .. the final efficiency of the locomotive is about 5.5% << ?
Oh , uhm – smoke box temps varied quite a bit depending on combustion rate , properties of coal , Lamda factor , effect of draughting and boiler design plus some further influences .
But , never mind , it’s a nice table just the same and with the distance of time we can appreciate in their heyday these engines were great tools for heavy RR work – and leave it at that .
Regards
= J =
Juniatha: ( when with a BB at work usually there was black smoke like a volcanic eruption ) ?
Veto! Hard working, I guess every steamloco acts like this.
Y6b and Class A were putting an equal amount of dark smoke, in a more brownish color, dispite the better heat content of coal.
4017
-edit-
Juniatha and Burgard 540,
however, BB's tendency for putting out a black smoke cloud from time to time maybe was caused by the grate's reduced air intake area, if I do understand this case correctly.
Keep in mind, how much smoke a steam locomotive puts out depends on a number of factors, such as the quality of the fuel used, either coal or oil, the physical condition of the locomotive, how well the fireman's doing his job, and how hard the engine's working. From looking at old photos and films sometimes I think the engine crews may have been "hamming it up" to make the engine look more dramatic, i.e. "Burning of Rome" smoke effects. Remember, the last thing management wanted to see was excessive smoke, lots of smoke meant poor combustion and poor fuel economy, all things being equal, of course. Hey, when I use the fireplace at home the last thing I want to see is a lot of smoke, it means I'm doing something wrong!
To Juniatha and Burgard,
you wrote:
each of these values would describe a certain work point of the engine , so how do you get from there to a general statement of overall locomotive efficiency of , quote >> .. the final efficiency of the locomotive is about 5.5% << ?
What about their chassis/gear effeciency:?
axles,,all rotating parts, cylinder, suspension, other stuff to avoid tendendies to frequency oscillatory vibrations , inherent with any rod-driven system. And then, a 200t 7axle-tender behind them??? You name more!
All I understand so far is, that cylinder hp minus drawbar hp was a loss at around ~10% (6680-6000 at ~ 40mph) . So it would increase the measured efficiency a little bit to Burgard's data of 5.5?
(But, hey, 90 percent gear effeciency? Is that cool?)
I dont have knowledge or enough background to interpret your table data into actual figures. But all looks pretty congruent with actual test data.
Juniatha,
A little bit of explanation might clear things up. Really only pay attention through lines 30 on the tables. After posting I noticed I left the 7.70% moisture in the Dry column on the fuel data. I gave a hydrogen content of the Rock Springs coal of 5% from data on similar coals. The only references for Rock Springs coal I have is the proximate analysis. If anyone has the ultimate analysis, please share.
Table 1 shows the inherent losses of heat in the combustion process even with perfect (stoichiometric) combustion, hence why I left the unburned, radiation and unaccounted for losses as zero. The losses are from: 1) heating the moisture in the fuel and water vapor produced from combustion of hydrogen, 2) humidity in the air, and 3) the heat lost in expelling the combustion gases at 700 degrees F, 660 degrees above the ambient air.
I wanted to see what these were before any other losses would be added in. This to me shows a huge limitation of the steam locomotive in that 18% of the heat of the fuel cannot be used at all. The inherent losses cannot be decreased expcept via drying the all coal prior to firing in the locomotive (expensive and not done) or through place some type of air preheater to try extract some heat from the expelled combustion gases (again not done on locomotives due to lack of space and complication, although in stationary plants this is done extensively cooling the gases to 350 degrees or so). I chose 700 degrees since I assumed that it would be a fair representation of conditions when the locomotive was working hard.
For Table 2, I added the unburned, radiation, and unaccounted for losses as well as increasing total air to 125% of theoretical. The 125% total air comes from Ralph Johnson's (pg 26-27) and others, 25% more air than theoretical (what the exact amount was allowed into the Big Boy's firebox during the test is unknown to me, it could be more). The table shows the calculation of the nearly 40% loss the heat content of the fuel.
The 80% absorption for the boiler is from a heat balance article by Lawford Fry. He reports that test data shows that regardless of firing rates or boiler design, the locomotive boiler absorbed about 80% of the heat produced from combustion (not to be confused with 80% of the heat content of the fuel).
The 11.5% cylinder conversion is from a simple calculation - assume steam entering the cylinders at 275 psig & 715 degrees, and leaves the cylinders at 30 psig and 325 degrees. Also, factor in a 10% mechanical loss and you get about 11.5% of the heat is converted to work at the drawbar. Johnson (pg 127) states that no more that 12% of the heat energy in the steam fed to the cylinders is converted to work and it is typically around 8%.
For the final efficiency use: 19400 lbs coal per hour at 12534 Btu/lb equals 2.431 x 10^8 total Btu's from the fuel; 5400 average drawbar horsepower equals (times 2545) 1.374 x 10^7 Btu's of work. Divide them and get 5.65% efficiency for the locomotive.
There's a lot of data needed to do eliminate the assumptions, like cut-off, actual steam chest pressure and temperature, combustion gas analysis, color of smoke, draft in firebox & smokebox, etc.
Really I'm just trying to use some educated assumptions to fit the test data, I'm not pulling figures out of my......
Page numbers refer to "The Steam Locomotive" by Ralph Johnson
Hi folks
BB 4017 , quote :
>> Veto! Hard working, I guess every steamloco acts like this. Y6b and Class A were putting an equal amount of dark smoke in a more brownish color, …<<
Nope – not every steam locomotive , only those with bad combustion , due to fuel fed at a rate draughting can’t deal with , or any other faulty handling or flawed condition of firebed . Anyways , many or few , that doesn’t make it better when it occurs . It’s still black smoke and black smoke is a visual sign of dramatically incomplete combustion .
>> .. brownish color ..<< : I say “Eeeeeehurrgh! smells awful !”
>> BB's tendency for putting out a black smoke cloud from time to time maybe was caused by the grate's reduced air intake area <<
Ok , you might say I wasn’t there – but from what my father said and from what it appears like on photos , heavy smoking was pretty regular with about any of the big steamers – Nines , CSA-I / II , BB , FEF-I / II / III or you name them . If it had been a special problem of the BBs caused by ‘reduced air intake at grate’ I’m pretty sure UP’s technical staff would positively have sorted it out . The problem was multiple rooted and since it started with the quality of coal itself and it’s handling , it would not have been easy to address , so it probably was just allowed to continue under the caption “we don’t care as long as coal is cheap” . As with so many incompletely resolved technical problems that plagued the steam locomotive right to the end of it’s development , this arguably was a questionable attitude back then – yet a comprehensible one . However , the longer the like was allowed to continue , the more severe became consequences for outlook of steam traction . In his book ‘The Red Devil and other Tales of from the Age of Steam’ Wardale severely accuses ‘good enough engineering’ prevailing with steam to have offered , quote >> the knife by the handle << to it’s abolition .
Firelock , quote :
>> Keep in mind, how much smoke a steam locomotive puts out depends on a number of factors, such as the quality of the fuel used, either coal or oil, the physical condition of the locomotive, how well the fireman's doing his job, and how hard the engine's working. <<
Sure – that’s why I wrote “ Apart from actual figures , each of these values would describe a certain work point of the engine ..”
>> I think the engine crews may have been "hamming it up" to make the engine look more dramatic <<
I guess so – it meant no extra work with a stoker , but it saved some care taking to just ‚put on plenty’ and let the boiler digest it somehow . D Wardale commented on ‚smoking contests’ leaving a certain yard and that his rebuilt #2644 was regarded ‘at disadvantage’ because it wouldn’t easily smoke and if so never reached the desired degree of density .
>> Hey, when I use the fireplace at home the last thing I want to see is a lot of smoke, it means I'm doing something wrong! <<
That’s right : you’re wrong – I mean if you did so . But you don’t and so it won’t – logical .
>> What about their chassis/gear effeciency:? <<
Now , that means shifting matters to the other extreme . As far as valve gear efficiency is concerned I have mentioned it : “ .. what was the adiabatic and the polytrophic heat drop , at what amount did you calculate wall effects and influences of cylinder tribology and what was c/o “ ( c/o for cut off ) As far as getting into influences of mechanical characteristics and running resistances by chassis design , for the purpose at hand I would consider these negligible since the engines regarded were from the same builder , to the same philosophy of design and realized with similar frames structural features .
>> other stuff to avoid tendendies to frequency oscillatory vibrations <<
Other than cross-balancing , there wasn’t much thought put into these aspects with steam locomotive design – unfortunately .
>> And then, a 200t 7axle-tender behind them??? You name more! <<
That’s where it ended : with power delivered at tender drawbar any further losses were not to blame on the locomotive !
>> cylinder hp minus drawbar hp was a loss at around ~10% .. But, hey, 90 percent gear effeciency? Is that cool? <<
Ooops – that’s power at wheel rim what you mean , unfortunately edbhp is a way bit further down because the locomotive first has to propel itself before delivering power at tender drawbar . With powerful yet heavy American 4-6-4 , 4-8-4 and equivalent types , self-propulsion at high speed including wind resistance could very well consume 50 % or more of indicated power output if an express engine listed ~ 1/2 of the mass of train consist behind the tender . In typical European Pacifics on average the balance was markedly worse because of lower total indicated power output , below or around 1/2 of said American engines .
That’s why without some substantial further increase of power output per unit of engine mass , demanding proportional increase of thermal efficiency , explicitly high speed traffic was becoming progressively expensive with classic steam above some 100 mph – in contrast the secret of efficiency of electric traction in high speed range as well as in highly dynamic train handling lies in its offering unparalleled power output per unit of engine mass . Again , that’s why I say for American RRs to overcome rising energy costs , to protect their competitiveness and to increase revenue earning total freight ton-miles production capacity on existing if upgraded lines , a complete and lasting answer can only be realized with large scale electrification .
Juniatha
thank you for your enlightening answer from the point of view of an engineer, ackknowledged.
J: Nope – not every steam locomotive , only those with bad combustion
I guess, then, all or most of them is therefore the right answer . North American steam locos attempted to be standarized .In this case I noticed that German engines have a very familiar appeal to their US big brothers. Regardless imperfection. My empathy for these designs is the inside/outside tension and expressional + feelable force of the machinery.
J: Ok , you might say I wasn’t there – but from what my father said and from what it appears like on photos , heavy smoking was pretty regular with about any of the big steamers –
my case, too. There are indeed some photos of the engines you named before, with no visible smoke at all, moving fast by photographer's comment (Otto Perry, Stan Kistler), as the opposite as well.
At least there must have been some certain agreements with the builders and the roads, how much average output should have been achieved with their designs. Some compromises were avoided, some not. - Maybe Burgard's attempt for calculations will fail, I encourage you for helping him ;-)
It is just a black box to me, the picture is blurred., with vast imagination of inside prozesses.
Outside seeing just a given mass of doing output work. at given circumstances.
Ok, a layman's question, how much effect would smokebox size and exh. nozzle shape have on exhaust temp? I know great thought went into these parts. It seems to me that there would be a 'best' speed for the exhaust to move through the flues, too fast would not give it time to transfer heat to the water, too slow would not give enough air for compleat combustion. Charles Mcshane's 'Classic American Locomotives' has a large section devoted to these desgines. They range from the very simple to the very complex. Were they worth the time and cost?
Rikers Yard Ok, a layman's question, how much effect would smokebox size and exh. nozzle shape have on exhaust temp? I know great thought went into these parts. It seems to me that there would be a 'best' speed for the exhaust to move through the flues, too fast would not give it time to transfer heat to the water, too slow would not give enough air for compleat combustion. Charles Mcshane's 'Classic American Locomotives' has a large section devoted to these desgines. They range from the very simple to the very complex. Were they worth the time and cost?
Heat transfer in fire tubes is by convection. The faster a fluid flows (exhaust gasses are a form of a fluid) through a heat exchanger (the tubes) the higher the rate of heat transfer. The faster, the better. However, as you try to push or pull more gasses through the tubes, you run up against the flow capacity of the tube (determined by the diameter and length of the tube), with resultant back pressure. This is why "late steam" designed in the 1940's generally used large diameter, shorter fire tubes than older designs from the 1930's.
It was determined through testing that the "ideal" flue length was right around 20' in length, with the diameter increased to 4" from the more typical 3.5" diameter found in older designs. This maximized gas flow, reduced back pressure, and maximized heat transfer. Additional flue length over 20' added next to nothing in heating capacity, and probably caused more harm than good by allowing the corrosive exhaust gasses to condensate in the tubes.
All combustion should be complete prior to the tubes as the oxygen content is too low in the tubes for additional combustion anyway. Late steam designs generally used the additional boiler space available from the shorter tube design to increase the fire box/combustion chamber length to increase combustion efficiency of the gasses prior to entering the tubes.
Late design locomotives using this engineering generally had much higher direct heating surface area (fire box / combustion chamber) where the majority of the steam is produced via radiative heating, and a much lower indirect heating surface (the tubes) than older designs. This often produced the illusion that late steam had "less" total heating surface than older designs, however the later designs had higher combustion efficiency, higher steam production in the larger firebox/combustion chamber, better heat transfer and higher superheater temperture in the fire tube section.
Thank you, learn somthing new every day! So the faster the "spent" gases move through the tubes the better, would this be true for the flues with the superheater tubes in them?
My Father was a fireman on the B&O here in Pa, he tells me that a uncorrected slip could "pull the fire off the grates and send it up the stack". It seems that this was "too much of a good thing". It seems that newer locos where more pron to this than older ones. Would the bigger flues promote this? [ He might have streched this a mite]
Rikers Yard,
To give you some numbers - doubling the rate of flow for the combustion gases through each tube or flue will increase the heat transfer via convection by about 90%.
Another reason for building larger fireboxes & combustion chambers is that the process of combustion ceases rather quickly after the gases enter the tubes because the temperature drops below the ignition temperature.
Ensuring proper combustion should be the dominant design characteristic since efficiency of the boiler as a whole is almost entirely dependent on the efficiency of fuel combustion. For example, an increase of 3% in combustion can increase the boiler efficiency by up to 25%.
Cheers - Joe
It won't be intuitive to some readers, so it might be worth explaining that heat transfer between two mediums, say steel tubes and surrounding water bath, works better the steeper the gradient of temperature between them. That is, heat transfers as the fourth power of the difference in heat content from the hotter medium to the cooler medium.
You might think that it would be best to slow the passage of the gases through the tubes so that all the heat could be recovered by the surrounding water bath in the boiler. You would want as little heat in the gases issuing into the smoke box at the far end of the tubes, right? Wrong! Because of this heat transfer law (a law posited by Messrs. Stefan and Boltzmann), saying that the thermodynamic heat of a radiating surface issues at the 4th power (not squared, not cubed, but fourtheth! , you are going to heat up the working medium, your water, many times more quickly and efficiently if you keep those tubes as close to red hot as you can keep them....constantly!
It is only further along when all that hot gas goes whooshing up the stack with the help of waste steam that we begin to see how the steam locomotive wastes a lot of energy.
I am not a physicist or an engineer, so I may stand some correction worth mentioning here, but I think for argument's sake I have the basics mostly right. I'll know soon....
Crandell
Burguard540,
So any thing to speed up the flow through the boiler would be worth the effort, within reason. Some of the efforts pictured in the book seemed to be overly complex, a maintence headache in the making. Maybe this is why U.S. builders didn't use these items for long, as European's did.
"Normal" people think I know everything about trains, but I am always learning more and am surprised at how much there is to learn.
Thanks, Tim
Selector,
Thank you, I should know that from high school science class, but its been a long time since high school. They demostraited this with 2 cups of water, 1 was warm [close to room temp] the other was hot [ close to boiling]. The question was witch cooled faster. The answer, the hot, due to the higher temperature gradient ! Witch is why you can't keep your tea warm in the deer stand or waiting for a train!
Tim
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